According to 'equery uses app-arch/pigz-2.3.3', the symlink USE flag will: 'Force kernel ebuilds to automatically update the /usr/src/linux symlink', but according to the ebuild code, this USE flag does something different: if use symlink; then dosym ${PN} /usr/bin/gzip dosym un${PN} /usr/bin/gunzip fi
Fixed in the tree.